The present invention generally relates to an apparatus and a method for calibrating the position of a cassette indexer in a semiconductor process machine and more particularly, relates to an apparatus and a method for calibrating the position of a cassette indexer by utilizing a calibrator equipped with a plurality of distance sensors for sensing the position of the calibrator, i.e. the position of a cassette indexer relative to a pre-calibrated wafer blade extended into a cavity in the calibrator.
In semiconductor fabrication technology, the continuous miniaturization in device fabricated demands stringent requirements in the fabrication environment control. When the feature size in the present fabrication environment is reduced to 0.25 xcexcm or smaller, i.e. to 0.18 xcexcm, a cleanliness class of at least 0.1 (particles per cubic meter) becomes necessary. One of the feasible methods for reducing contamination in environmental control is the utilization of an inert mini-environment. For instance, in order to eliminate micro-contamination and to reduce native oxide growth on silicon wafers, the loading/unloading procedures of a process tool is enclosed in an extremely high cleanliness mini-environment which is constantly flushed with ultra-pure nitrogen without oxygen or moisture.
A typical mini-environment utilized in contamination control is a SMIF (standard mechanical interfaces) apparatus. A wafer cassette can be transported into a process tool through an enclosure known as a SMIF pod situated on top of a SMIF apparatus.
Another form for utilizing SMIF is a SMIF indexer, as shown in FIG. 1. Typically, in the process equipment 10, a wafer cassette 12 can be handled by either a SMIF arm (not shown) or a SMIF indexer 20 for transporting wafers into the process machine 10 for processing. The wafer cassette 12 is first lowered by the indexer 20 into a transport position, as shown in FIG. 1, a wafer blade (not shown) is then extended into the wafer cassette for unloading a wafer from the cassette. The accurate movement and positioning of the cassette indexer 20 is therefore of upmost importance, since any mispositioning of the indexer would cause severe damage to either the wafer blade, the wafer cassette 12, or both. When the indexer is mispositioned, the wafer blade may also strike a wafer and cause wafer breakage. Conventionally, the positioning of the cassette indexer 20 is calibrated by visual examination and therefore, is grossly inaccurate and operator-dependent. Calibration performed by using wafer cassettes fabricated of a plastic material fails to produce accurate calibration since plastic cassettes may be easily deformed. To achieve accurate calibration, a calibrator must be fabricated of a rigid, non-deformable material. The calibrator must also not differ from a SEMI standard. (Semiconductor Equipment and Materials International, 805 E. Middlefield Rd., Mountain View, Calif.).
It is therefore an object of the present invention to provide an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine that does not have the drawbacks or shortcomings of the conventional calibrating apparatus.
It is another object of the present invention to provide an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine that is fabricated of a non-deformable metallic material.
It is a further object of the present invention to provide an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine that is installed with a plurality of distance sensors.
It is another further object of the present invention to provide an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine that is constructed on a SEMI standard fitted base plate.
It is still another object of the present invention to provide an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine that is equipped with at least two spaced-apart rows of distance sensors.
It is yet another object of the present invention to provide an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine that is equipped with a processor for receiving signals from a plurality of distance sensors capable of calculating the levelness of a wafer blade positioned in the apparatus.
It is still another further object of the present invention to provide an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine that is capable of determining both the front-to-back tilt and the side-to-side tilt of a wafer blade positioned in a cavity of the apparatus.
It is yet another further object of the present invention to provide a method for calibrating the positioning of a cassette indexer in a semiconductor process machine by determining the levelness of a wafer blade extended into a calibrator utilizing a plurality of distance sensors.
In accordance with the present invention, an apparatus and a method for calibrating the position of a cassette indexer in a semiconductor process machine are provided.
In a preferred embodiment, an apparatus for calibrating the position of a cassette indexer in a semiconductor process machine is provided which includes a base plate that has a rectangular shape, a uniform thickness and parallel upper and lower surfaces; a top plate that has a uniform thickness and parallel upper and lower surfaces, the top plate has the same shape and size of the base plate; at least two support members for rigidly attaching the top plate to the base plate in a parallel relationship, the two support members being positioned opposite to each other forming a cavity therein; at least two spaced-apart rows of distance sensors each having at least five distance sensors mounted on the lower surface of the top plate for sensing a distance in the cavity, wherein a sensor in a front row and a corresponding sensor in a back row sense a front-to-back tilt while two adjacent sensors in the same row sense a side-to-side tilt of a wafer blade extended into the cavity of the apparatus; and a processor for receiving signals from the distance sensors and for calculating the front-to-back and side-to-side levelness of the wafer blade such that a levelness of the cassette indexer can be determined.
In the apparatus for calibrating the position of a cassette indexer in a semiconductor process machine, the base plate may be a SEMI standard fitted base plate. The base plate, the top plate and the at least two support members may be fabricated of a dimensional stable, rigid material, or may be fabricated of aluminum. The apparatus formed by the base plate, the top and the at least two support members may have a dimension substantially the same as a wafer cassette. The apparatus may further include at least two spaced-apart rows of distance sensors each having at least seven distance sensors. The at least five distance sensors may be optical sensors, or may be sonic sensors. The cassette indexer may be further equipped with an elevating device. The position of the wafer blade may be calibrated before being extended into the cavity of the apparatus. The wafer blade may be extended into the cavity of the apparatus in a direction that is parallel to a base of the process machine. The processor may further include a display unit to graphically indicate the positioning of the wafer blade.
The present invention is further directed to a method for calibrating the positioning of a cassette indexer in a semiconductor process machine which can be carried out by the operating steps of first providing a calibrator formed by a base plate, a top plate and at least two support members rigidly attached to the top plate and the base plate in a parallel relationship and opposite to each other; the base plate may have a rectangular shape, a uniform thickness and parallel upper and lower surfaces; the top plate may have a uniform thickness, parallel upper and lower surfaces and the same shape and size of the base plate; providing at least two spaced-apart rows of distance sensors each having at least five distance sensors for mounting to the lower surface of the top plate for sensing a distance in the cavity; positioning the calibrator on top of a cassette indexer; extending a pre-calibrated wafer blade into a cavity of the apparatus; sensing a front-to-back tilt of the wafer blade by a sensor in a front row and a corresponding sensor in a back row; sensing a side-to-side tilt of the wafer blade by two adjacent sensors in the same row; sending signals from the distance sensors to a processor and calculating a front-to-back levelness and a side-to-side levelness of the wafer blade; and determining a levelness of the cassette indexer.
The method for calibrating the positioning of a cassette indexer in a semiconductor process machine may further include the step of providing a display unit in the processor to graphically illustrate the levelness of the wafer blade. The method may further include the step of sensing a distance in the cavity by the at least five distance sensors by an optical means, or by the at least five distance sensors utilizing sonic means. The method may further include the step of correcting the levelness of the cassette indexer based on signals received by the processor.